title: Amphidynamic crystals of a steroidal bicyclo[2.2.2]octane rotor: a high symmetry group that rotates faster than smaller methyl and methoxy groups.
abstract: The synthesis, crystallization, single crystal X-ray structure, and solid state dynamics of molecular rotor 3 provided with a high symmetry order and relatively cylindrical bicyclo[2.2.2]octane (BCO) rotator linked to mestranol fragments were investigated in this work. By use of solid state (13)C NMR, three rotating fragments were identified within the molecule: the BCO, the C19 methoxy and the C18 methyl groups. To determine the dynamics of the BCO group in crystals of 3 by variable temperature (1)H spin-lattice relaxation (VT (1)H T1), we determined the (1)H T1 contributions from the methoxy group C19 by carrying out measurements with the methoxy-deuterated isotopologue rotor 3-d6. The contributions from the quaternary methyl group C18 were estimated by considering the differences between the VT (1)H T1 of mestranol 8 and methoxy-deuterated mestranol 8-d3. From these studies it was determined that the BCO rotator in 3 has an activation energy of only 1.15 kcal mol(-1), with a barrier for site exchange that is smaller than those of methyl (E(a) = 1.35 kcal mol(-1)) and methoxy groups (E(a) = 1.92 kcal mol(-1)), despite their smaller moments of inertia and surface areas.
authors.affiliation: Department of Chemistry and Biochemistry, University of California at Los Angeles, Los Angeles, California 90095-1569, United States.
authors.forename: Braulio
authors.initials: B
authors.lastname: Rodríguez-Molina
authors.forename: Salvador
authors.initials: S
authors.lastname: Pérez-Estrada
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Garcia-Garibay
mesh_terms: D001643:Bridged Bicyclo Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy; D008656:Mestranol / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D013696:Temperature
chemical_list: D001643:Bridged Bicyclo Compounds; D008656:Mestranol